1. I haven't had any major issues with this. Take a look in the UV Texture Editor before and after converting to SubD to see what I mean...

2. Creasing does have some nasty effects on mapping. Kind of hard to explain but for example I had to do some extra partial creasings on the wheel house of my Andrea Gail project just to keep the UVs not stretching. Creasing does not modify the UVs which is kind of odd if you ask me... Anyway at work-in-progress stage I don't do creases at all (I usually know where they will be in the end). I convert back to polys using level 0 vertices.

3. This is what I usually do:
a.0. (optional) start with nurbs
a.1. model in poly's and check and tweak (only level 0 vertices if at all) using subd.
b. map the UVs
c. convert to SubD and add creases for lighting and rendering.